In view of numerous factors such as higher energy prices and environmental concerns, the production of value-added gaseous products from lower-fuel-value carbonaceous feedstocks, such as biomass, coal and petroleum coke, is receiving renewed attention. The catalytic gasification of such materials to produce methane and other value-added gases is disclosed, for example, in U.S. Pat. Nos. 3,828,474, 3,998,607, 4,057,512, 4,092,125, 4,094,650, 4,204,843, 4,468,231, 4,500,323, 4,541,841, 4,551,155, 4,558,027, 4,606,105, 4,617,027, 4,609,456, 5,017,282, 5,055,181, 6,187,465, 6,790,430, 6,894,183, 6,955,695, US2003/0167961A1, US2006/0265953A1, US2007/000177A1, US2007/083072A1, US2007/0277437A1 and GB1599932.
Reaction of lower-fuel-value carbonaceous feedstocks under conditions described in the above references typically yields a crude product gas and a char. The crude product gas typically comprises an amount of particles, which are removed from the gas stream to produce a gas effluent. This gas effluent typically contains a mixture of gases, including, but not limited to, methane, carbon dioxide, hydrogen, carbon monoxide, hydrogen sulfide, ammonia, unreacted steam, entrained fines, and other contaminants such as COS. Through processes known in the art, the gas effluent can be treated to remove carbon dioxide, hydrogen sulfide, steam, entrained fines, COS, and other contaminants, yielding a cleaned gas stream comprising methane, carbon monoxide, and hydrogen.
For some applications, it may be desirable to recover a gas stream that is enriched in either methane or hydrogen gas. In some situations, it may even be desirable to recover a gas stream that almost entirely comprises methane or hydrogen. In such situations, the cleaned gas stream must undergo additional processing to remove carbon monoxide. This additional processing can complicate the recovery of methane and/or hydrogen, especially if there is no need to recover a gas stream comprising appreciable quantities of carbon monoxide. Thus, there is a need for processes which can obviate the need to treat a cleaned gas stream to remove carbon monoxide.